Railway signalling systems known in the art provide power supply in the control means with a filtration or rectification device particularly when the power supply is AC. LED being a DC driven device is also known to provide spike protection devices across the power supply line. While such devices have their uses, the use of such devices can itself result in unsafe conditions in the signalling circuits due to leakage, partial failure and the like. Leakage in such devices results in the current being drawn by the leakage resulting in the LED's not being lit, while simulating a lit up signal. LED signal lamps comprise of a cluster of LED's in series or parallel combination. Each series cluster may have an independent current regulator to prevent unequal current distribution through the cluster. However, without an overall feedback system, meaningful protection against failure is not feasible. It is known in the art to provide LED's in series combination with one or more shunts so that failure of one LED does not affect the other LED's in the cluster. However, this can result in reduction in the intensity of the beam. Also, in a condition where more than one LED has failed, a condition of poor visibility and/or unsafe conditions are created, since the shunts may be drawing current, but the LED cluster is not emitting adequate light.
Provision of a shunt by way of providing a parallel resistance across each series LED can be used to prevent failure of series of LED cluster in the event any one LED has failed in the unit. This, however, requires substantial power dissipation in the shunt resistances. This is further aggravated in the event the voltage jump allowable/cushion available is not substantial. Thermal control/dissipation means can be provided on LED lead/pad on the copper side of the printed circuit board/large copper area for each solder pad, for heat sinking to provide higher light output and improve temperature performance. However, the heat builds up in the enclosure over a period of time thereby affecting its performance.
A significant use of LED signal lamps is in the Railways which use high voltage traction where cables carrying drive to the lamps get induced voltage and may light up the signal when not intended to be lit. There can be a partial failure which may further lead to a complete failure. It is not desirable to have blanking of signals or unwanted signal lit.
LED signal lamps are desirable alternatives to filament bulbs used in signalling applications in order to reduce the maintenance, bulb fusing related problems as well as for lowering the energy costs. The use of LED's also enables the reduction in size of the signal housing. Another advantage of using LED's is that the use of secondary optics can also be avoided.
Reference is drawn to Indian Patent No. 199890 which discloses an architecture of the improved LED signal using Fail Safety device. However, this document does not provide the configuration of distinct domain arrangement of the control and monitored function as disclosed in the present invention.
US 20160081152 discloses generating a voltage feedback signal in non-isolated LED drivers, however, this document does not provide the configuration of distinct domain arrangement of the control and monitored function as disclosed in the present invention.
EP 2687418 discloses LED track signal for rail transport and interface for such an LED track signal, however, there is no disclosure of domain distinction method provided by this document.
None of the prior documents disclose sequencing of control and/or monitoring functions to improve the integrity, safety and reliability in the control system as disclosed in the present application.
A conventional LED based signalling system comprises a unit for supplying a signal. The signal supply unit provides either an ON signal or an OFF signal. In the presence of an ON signal, the aspect (which is comprised of a cluster of LEDs) is required to glow. In the presence of an OFF signal, the aspect should not glow. In one of the configurations, the absence of an ON signal can be considered as an OFF signal and similarly, vice versa. The signal from the signal supply unit is provided to the aspect (lighting unit) at location through a series of devices whose functionality is to detect failure in the proper operation of the aspect in indicating the appropriate signal.
More particularly, a first component identified as “Series Lamp Checking Relay (ECR)”, a second component identified as “Health Monitoring Unit (HMU)” and a third component identified as “Current Regulator (CR)” are coupled between the signal supply unit and the aspect at location. The ECR comprises a series relay whose function is to validate presence of the appropriate signal in the line between the signal supply unit and HMU. If the appropriate signal is not present in this part of the line, the ECR should inform the signalling system.
It may be noted that in order to operate the ECR it is required to supply high level of current while to drive the LED current, substantially low level of current is required. Thus, to drive both the aspects at location and the ECR, a separate component identified as CR is used. As can be noticed, the CR comprises a LED driver circuit which supplies the appropriate driving supply to the aspect and comprises a relay driver load which is able to generate the suitable condition which upon detection by Line Proving Sensor (LPS) leads to triggering of the ECR.
The aspect at location comprises, at least, one optical feedback mechanism to determine as to whether the aspect is outputting the proper signal or not. By way of example, the relay driver load may be brought into action depending upon the output of the optical feedback mechanism.
However, in the above described system, there exists a possibility of not having a correspondence between the signal and the ECR during earthing, cable faults and other conditions.
Also, the power drop across the cable which is commonly referred to as cable drop is substantially very high (because of the high level of the current flowing through cable). Thus, the amount of energy spent is substantially high.
Also, induction of electrostatic field in the current carrying conductors is a difficulty in the commonly available system.
Thus, despite the above described improved versions of lamping system which use LEDs, it is still required to provide further systems which are more efficient and address at least some of the above drawbacks of the above identified systems.
In railway signalling, the signals are proven to operate them in an interlocked manner. In such cases, safety requirements also focus on:                proving of the signal which is done by sensing its load which may lead to picking up of the Relay (ECR). Existence of a load without signal being lit is considered unsafe and this may lead to incorrect communication to the train driver.        blanking of signal i.e. a signal meant to be lit but not lit can lead to disruption in Rail operation or missing of signal by the driver which is also unsafe.        
The above conditions when translated to LED signals require:                LED's may not fail as short circuit. Thus, reverse polarity or overdrive conditions are not safe.        LED array (LEDs in series) may be more than one so that failure of any array does not lead to signal blanking.        any protection or controls in the system must be stable with temperature variations.        fail safety may lead to open circuit conditions or partial failure indication. It is not desirable that an aspect is lit when not selected or unlit aspect is proven as lit.        
Current LED signals are a retro fitment in the bulb signal lighting circuit and are provided with blanking and non-blanking functions with latching, which was not there in bulb lit signals.
LED signals perform over a time span of 10 years as compared to bulb signals which have a time span of few months. This requires HMU for predictive maintenance. However, HMU is no longer kept in circuit due to fuse blowing caused by accidental shorts during maintenance work and the related work of setting it right.
The light output of a bulb is directly related to the current drawn. In bulb lit proving circuits, use of series current sensed lamp checking relay is suitable.
In LED signal the current is not directly related to the light output. Use of current sensed series ECR is not the desirable solution in this safety application. The current operated ECRs require far greater current than needed for the signal illumination by LEDs. However, this is mandated as the LED signals are retrofitted in existing signal circuits. Thus, though LED lighting requires only about 3W, the rest is dissipated in the unit.
The present LED signals are mostly AC lit, thus, they have AC noise immunity of about 60V through electronic cut-off, and thus require use of cutting-in relay circuit as a protection against false lighting due to induced voltage, adding to cost and affecting availability.
The present LED signals have limited protection ability to withstand extraneous voltage and would fail above 200 VAC (MOV of 175 VAC). In field conditions with over and above the 110 VAC used to light up the selected signal there can be additional induced AC voltage of 100 Volts/km. Thus, there can be conditions where the voltage applied to selected signal is enough to damage it. Many signals have been received from the field with input stage burnt.
The present LED signals are not immune to cable fault. A short in cable will lead to wrong side failure.
The signals internally operate on DC and being operated on AC supply requires the use of Bridge Rectifier and Filter Capacitor, MOV as devices across the line the failure of which can lead to wrong side failure.
The signal is proven at the signal post only and it is indirectly proven at the station by sensing the cable current which constitutes the signal current and any other leakage current in the cable. The specification requires that if the signal current, which may not be directly related to the signal illumination, is required to be operated in a certain window else the signal should be latched to blanking or non-blanking condition. Thus, any electrical disturbance to a steadily lit selected signal can cause it to latch and cause disruption in train operation. When a train is passing such electrical disturbances may be created, besides vibration/change in pressure of relay contacts in the field.
The degradation in LED illumination over the life span of the signal is a definite phenomena. In view of the above, it is preferable that since the original HMU is also not being used the lamp proving may not be based on current sensing only.
LED signal use electronic/electrical components. Dissipation in circuit should be minimized to improve reliability.
The LED signals use electronic circuits. The cable from cabin to signal is also an integral part of the lighting circuit. Lamp proving should be immune to cable faults.
Bulb lit signals are self-restoring and current LED signals are not.
The 2003 SSC (Signals Standards Committee) decided that non-dissipative LED main signals should be developed, and till such time the current regulator unit used should be a separate unit as it carries the dissipation of 80% of the power consumed and exceptional heating in the limited space available, which is not suitable for the LEDs and overall reliability of the product, cost of maintenance, inventory, etc. The proving/safety methods required use inhibiting functions like blanking and latching. It was seen as a limitation as compared to self-restoring fail safe filament bulb. Today, significant percentage of the failures of LED signals are due to blanking, non-blanking/latching, etc.
Present signals operating on LED ECR effectively load 22-25 W on the railway system per lit aspect including signal transformer, inverter, etc. losses. Signalling cables have AC leakage/induced current which can be as high as 40 ma after the use of cutting in relays. Thus, operating current of existing type of signal has to be kept quite high so that its normal functioning is not affected by leakage/induced AC current. This also increases the cable drop and reduces the signal distance. The inverter, signal transformer failure also contributes to signal failure.
Thus, to overcome the drawbacks of earlier systems, the present invention provides an improved control system for lamps with one or more driven unit, thereby improving efficiency, availability, reliability and safety of operation by facilitating reduction in energy consumption, capital costs, and maintenance costs in various systems operating and monitoring various electrical loads such as LED based lighting systems, logically integrating remote units, etc., by segregating the domains of various functions critical to maintain high level of system operation integrity and transporting a proven, monitored function through a medium to another location and for using the received proven function information to further prove the function at the receiving location with the functional requirements of the receiving location, entire operation being online and/or periodically reciprocated/handshaked which is further explained in detail herein below.